TW202238716A - Selective etching with fluorine, oxygen and noble gas containing plasmas - Google Patents

Abstract

A method for processing a substrate that includes: loading the substrate in a plasma processing chamber; performing a cyclic plasma etch process including a plurality of cycles, where each cycle of the plurality of cycles includes: generating a first plasma from a first gas mixture including a fluorosilane and oxygen; performing a deposition step by exposing the substrate to the first plasma to form a passivation film including silicon and fluorine; generating a second plasma from a second gas mixture including a noble gas; and performing an etch step by exposing the substrate to the second plasma.

Description

Selective etching using plasma containing fluorine, oxygen and rare gases

The present invention relates generally to systems and methods for semiconductor fabrication and, in particular embodiments, to systems and methods for selective plasma etching using plasmas containing fluorine, oxygen, and noble gases. [Cross-reference to related applications]

This application claims the rights of U.S. Provisional Patent Application No. 63/126,951, filed December 17, 2020, and U.S. Provisional Patent Application No. 63/194,561, filed May 28, 2021, which is incorporated herein by reference.

In general, the fabrication of semiconductor devices is performed by processes based on lithography, growth of passivation layers, and etching to achieve the desired structure of the target device consisting of layers of dielectric, conductive, and semiconductive elements . In the modern semiconductor industry, the etching step relies on reactive ion etching using plasma, mainly because of the fast etching speed and directional removal. However, with the development of manufacturing technology, when the size of logic elements continues to decrease below the scale of 10 nm, the accuracy required in dimensions (such as line width, etch depth, and film thickness) increases, and the conventional etch method challenges.

Wet etching is commonly used to achieve highly selective etching. For example, hot phosphoric acid is used to isotropically remove silicon nitride with high selectivity to silicon dioxide and silicon. However, in many applications anisotropic etching must be used and wet etching therefore cannot be used.

Against this background, in the development of etching technology, atomic-scale etching control and material selectivity during etching processing have become more important. Atomic layer etching (ALE) is a new technology that has been researched and is under development, and has advantages in atomic scale etching. ALE removes thin layers of material layer by layer based on sequential self-limiting reactions. However, in order to meet the current semiconductor industry requirements for realizing precise thin-layer architectures, ALE technology needs to be further developed to achieve the desired dimensional control and thin-film integrity with atomic precision.

According to an embodiment of the present invention, a method for processing a substrate includes: loading the substrate in a plasma processing chamber; performing a cyclic plasma etching process including a plurality of cycles, wherein each cycle of the plurality of cycles includes: A first plasma is generated from a first gas mixture; a deposition step is performed by exposing the substrate to the first plasma to form a passivation layer comprising silicon and fluorine; a second plasma is generated from a second gas mixture comprising a rare gas plasma; and performing an etching step by exposing the substrate to a second plasma.

According to an embodiment of the present invention, the method for processing a substrate includes: obtaining a substrate including a first region, a second region, and a third region, the first region includes a nitride of the first element, and the second region includes a nitride of the first element. oxide, and the third region includes an elemental form of the first element; and selectively etching the first region relative to the second and third regions by using a multi-step plasma treatment in a plasma processing chamber, the multi-step The plasma treatment includes exposing the substrate to a first plasma generated from a first gas mixture comprising silane, a fluorine-containing gas, and oxygen while maintaining the substrate at a first temperature, the first temperature being less than or equal to 0 °C; and while maintaining the substrate at a second temperature, exposing the substrate to a second plasma generated from a second gas mixture including a noble gas.

According to an embodiment of the present invention, the method for processing a substrate includes: obtaining a substrate including a first region, a second region, and a third region, the first region includes a nitride of the first element, and the second region includes a nitride of the first element. oxide, and the third region includes an elemental form of the first element; and selectively etching the first region relative to the second and third regions by using a plasma treatment, the plasma treatment comprising: While exposing the substrate to a plasma generated from a gas mixture including silicon, fluorine, oxygen, and a rare gas, the first temperature is lower than or equal to 0° C. while simultaneously at a temperature.

Plasma etching plays a key role in semiconductor manufacturing, and the need for precise atomic-scale control of the etching process has been increasing. Atomic layer etching (ALE), capable of removing material layer by layer, is a promising etching technique. However, to replace conventional etching techniques, ALE may require further improvements in quality factors in etching such as etch rate, selectivity, and anisotropy.

Many etching applications involve selectively etching one material without removing another. An example of such an application is the selective removal of silicon nitride (Si ₃ N ₄ ). Silicon nitride is widely used in semiconductor manufacturing, mainly as a dielectric and mask material. Therefore, the removal of silicon nitride without damaging other components such as silicon (Si) and silicon dioxide (SiO ₂ ) has significant industrial relevance. Since multiple surface materials are exposed to plasma etching, conventional etching processes use, for example, CF ₄ /H ₂ , CF ₄ /O ₂ /N ₂ , SF ₆ /O ₂ /N ₂ , SF ₆ /CH ₄ /N ₂ , SF ₆ /H ₂ /Ar/He, SF ₆ /CH ₄ /N ₂ /O ₂ , and other multi-component mixtures. Despite such optimization, the selectivity between silicon nitride and silicon may be about 4-6, and the selectivity between silicon nitride and silicon dioxide may be only 1.5-2. However, this may not be sufficient for many applications, and increased reactivity may damage the device element being formed. Example applications include silicon nitride spacer etch in self-aligned multiple patterning, and removal from O/N/O/N stacks (stacked layers of oxide and nitride) after high aspect ratio contact dielectric etch processes Silicon nitride, which can facilitate the fabrication of 3D semiconductor devices, including three-dimensionally arranged memory cells such as 3D vertical NAND (VNAND) memory structures.

Embodiments described in this disclosure provide quasi-ALE methods, or gas pulse etching, that may be advantageous in selectively removing certain materials over other materials. In many embodiments, the method includes a set, or multiple cycles, of two plasma treatment steps: a deposition step and an etching step. The deposition step is to deposit a layer comprising silicon oxyfluoride which acts as a passivation layer during the etching step. One or more plasmas containing fluorine, oxygen, or a noble gas may be used for these two steps in the example methods. The inventors of this application have discovered that the temperature dependence of the deposition rate and composition during the first plasma treatment step for deposition can lead to a temperature dependence of the etch rate during the second plasma treatment step for etching . These temperature dependencies are a function of the type of material exposed to the plasma. Based on these temperature dependent properties, a selective etch of one material relative to another is performed as will be explained in more detail in the following examples. Embodiment methods may advantageously enable selective etch processes, especially for nitride materials, such as silicon nitride, on oxide and/or substrate materials (eg, silicon oxide and/or silicon). In many embodiments, based on the temperature dependence of deposition and etch, the selectivity of the embodiment methods may be improved by utilizing low process temperatures, eg, lower than or equal to 0°C. Additionally, in some embodiments, the deposition and etching steps may be combined and performed as a single step. In addition, hydrogen-containing plasmas may also be used alone or in conjunction with an etching step to further improve overall etch performance including selectivity.

In the following, FIG. 1A first illustrates an example plasma system for processing substrates according to various embodiments. Exemplary diagrams of an example method of plasma processing comprising a deposition step using a first plasma and an etching step using a second plasma are illustrated with reference to FIGS. 2A-2F . Two example applications in which nitride can be selectively etched using an embodiment method are illustrated in FIGS. 2G-2J. A first embodiment of cyclic plasma treatment may be performed using fluorosilane and oxygen for the first plasma of the deposition step as shown in FIG. 3A. In the second embodiment shown in FIG. 3B , the fluorosilane may include hydrofluorosilane. As shown in Figure 3C, in an alternative embodiment, the first plasma may be generated from a gas mixture comprising silane, a fluorine-containing gas, and oxygen. In a further embodiment, the first and second plasmas (ie, the plasmas used for deposition and etching) can be used simultaneously in a single step. In conjunction with plasma, a continuous plasma treatment as shown in Figure 4A is achieved. Furthermore, as shown in FIG. 4B , a cyclic embodiment in which hydrogen treatment and plasma treatment using a combined plasma are cyclically repeated is also realized. Other embodiments using hydrofluorosilanes or silanes are illustrated in Figure 4C. Exemplary data obtained according to one embodiment is presented in Figures 5A-5C, 6A-6B, 7, and 8A-8B.

Referring to FIG. 1A , an example plasma processing system 100 includes a plasma processing chamber 120 connected to a gas delivery system 130 and a vacuum pumping system 140 . Gases may be introduced into the plasma processing chamber 120 through a gas delivery system 130 .

A substrate 110 , such as a semiconductor wafer to be processed, may be mounted on a substrate holder 164 within the plasma processing chamber 120 . In one or more embodiments, the substrate 110 includes one or more layers of silicon (Si), silicon oxide (SiO ₂ ), or silicon nitride (Si ₃ N ₄ ). In some embodiments, the substrate 110 may include a semiconductor wafer. Substrate 110 may also comprise any (stoichiometric or non-stoichiometric) compound including oxides and nitrides of Si, Ge, B, W, Al, Ti, Ga, Ta, Hf, or Zr. Substrate 110 can be patterned to include a number of features.

The substrate holder 164 may be a circular electrostatic chuck. Substrate 110 may be maintained at a desired processing temperature using a controller such as temperature controller 150 coupled to cooler 166 and substrate holder 164 .

In the illustrative example of FIG. 1A , substrate holder 164 is connected to first RF power supply 180 and may be a bottom electrode, while top electrode 162 is connected to second RF power supply 160 to power plasma 170 within plasma processing chamber 120 . In many embodiments, the top electrode 162 may be a conductive coil positioned above the top ceramic window, outside the plasma processing chamber 120 .

The configuration of the plasma processing system 100 described above is merely an example. In alternative embodiments, numerous alternative configurations may be used for plasma processing system 100 . For example, inductively coupled plasma (ICP) can be coupled with RF source power coupled to a planar coil on the top dielectric lid, or capacitively coupled plasma (CCP) generated using a disk-shaped top electrode in plasma processing chamber 120 Used together, the gas inlet and/or gas outlet may be coupled to a side wall or the like. Pulsed RF power and pulsed DC power (instead of continuous wave RF power) may also be used in certain embodiments. In various embodiments, RF power, chamber pressure, substrate temperature, gas flow rate, and other plasma processing parameters may be selected according to a corresponding processing recipe. In some embodiments, the plasma processing system 100 may be a resonator, such as a helical resonator.

Although not illustrated herein, embodiments of the present invention are also applicable to remote plasma systems as well as batch systems. For example, a substrate holder may be capable of supporting multiple wafers that rotate about a central axis as they pass through different plasma zones.

Processing of the substrate 110 within the plasma processing system 100 will now be described using FIGS. 2A-2J and 3A-3C. Figures 2A-2C show schematic cross-sectional views of a substrate during steps of plasma treatment, according to an embodiment, and Figures 2D-2F show another example, according to an alternative embodiment. Figures 3A-3C show process flow diagrams to perform the steps illustrated in Figures 2A-2H, and are described together below. 2G-2J illustrate two example applications of plasma processing to selectively remove nitride material during semiconductor device fabrication.

In FIG. 2A, an incoming substrate 110 to be processed is loaded into the plasma processing chamber 120 in FIG. 1A (see also block 300 in FIGS. 3A-3C). In one embodiment, the substrate 110 includes a nitride layer 212 to be etched by plasma treatment of the embodiment method. Also, in Figure 2D, access to the substrate 110 is shown, but comprising an oxide layer 214 instead of nitride.

To begin the deposition step, a first plasma is generated from a first gas mixture comprising fluorosilane and oxygen (eg, block 304A in FIG. 3A ). In various embodiments, the fluorosilane may include tetrafluorosilane (SiF ₄ ), such that the first gas mixture includes tetrafluorosilane (SiF ₄ ) and oxygen (O ₂ ). In other embodiments, the fluorosilane may comprise hydrofluorosilane (eg, block 304B in FIG. 3B ). Hydrofluorosilanes may have the formula _SixHyFz , where _x ≠0, _y ≠0, and z≠0. For example, hydrofluorosilane may include trifluorosilane (SiHF ₃ ), difluorosilane (SiH ₂ F ₂ ), or fluorosilane (SiH ₃ F). Both fluorosilane and oxygen are used as precursors for the passivation layer 213 comprising silicon oxyfluoride in Figures 2B and 2E.

In an alternative embodiment, the first gas mixture includes silane, a fluorine-containing gas, and oxygen (eg, block 304C in FIG. 3C ). Silicon and fluorine are provided separately with different precursors compared to the previous embodiments. By separately providing silicon and fluorine to the first plasma, the chemical composition of the passivation layer (eg, the ratio of silicon to fluorine) can be advantageously adjusted. Silanes may have the formula _SixHy , where _x ≠0 and y≠0. In some embodiments, the silane may comprise monosilane (SiH ₄ ). Fluorine-containing gases may include tetrafluoromethane (CF ₄ ), difluorine (F ₂ ), nitrogen trifluoride (NF ₃ ), sulfur hexafluoride (SF ₆ ), hexafluoroethane (C ₂ F ₆ ), octane Fluorocyclobutane (C ₄ F ₈ ), perfluoroisobutene (C ₄ F ₈ ), fluoroform (CHF ₃ ), or hydrogen fluoride (HF).

The use of a hydrogen-containing silane compound such as hydrofluorosilane or monosilane as described above may also advantageously provide a hydrogen-containing plasma during cyclic plasma processing, which may facilitate improved etch selectivity. Therefore, in some embodiments, selective treatment with a hydrogen-containing plasma to improve etch selectivity described below may be skipped.

In addition, although certain example methods described above (eg, FIGS. 3B and 3C ) do not dispense tetrafluorosilane (SiF ₄ ) into the processing chamber, the SiF ₄ species can advantageously be Different species react to produce in situ.

The process may be operated at a total gas flow into the plasma processing chamber 120 of between 1 sccm and 1000 sccm while maintaining the plasma processing chamber pressure between 1 mTorr and 1 atm. One or more inert gases may be added as admixtures to the first in the gas mixture.

In one or more embodiments, a separate additional treatment with a hydrogen-containing plasma may be performed before or during any cycle of the deposition-etch process. Referring to Figures 3A-3C, the steps of generating a plasma containing hydrogen (block 302) and exposing the substrate to the plasma containing hydrogen (block 303) may be inserted. In one or more embodiments, using a gas mixture comprising hydrogen (H ₂ ) or hydrogen fluoride (HF), or ammonia (NH ₃ ), and Ar, He, nitrogen (N ₂ ), or Xe in any proportion is performed Additional hydrogen-containing plasma treatment. In particular, any ratio of hydrogen:hydrogen fluoride:ammonia can be used. Alternatively, one or more inert gases including argon, helium, nitrogen, or xenon in any proportion may be used. Such additional treatment with a hydrogen-containing plasma can advantageously reduce the surface of the substrate, which can improve the selectivity of the deposition step.

In certain embodiments, an additional optional gas comprising hydrogen may be added to the first gas mixture. In other words, the steps illustrated in blocks 302, 303 may be performed together with the steps illustrated in blocks 304A, 304B, or 304C. Such an embodiment may advantageously reduce the number of steps in the plasma treatment and shorten the treatment time. A gas mixture containing hydrogen (H ₂ ) or hydrogen fluoride (HF), or ammonia (NH ₃ ), and Ar, He, nitrogen (N ₂ ), or Xe can be used as the additional gas in any proportion. In particular, any ratio of hydrogen:hydrogen fluoride:ammonia can be used. Alternatively, one or more inert gases including argon, helium, nitrogen or xenon in any proportion may be used.

In one embodiment, to power the first plasma, high frequency (HF) power between 1 W and 10,000 W may be applied to the substrate holder 164, and low frequency (HF) power between 0 W and 10,000 W may be applied. LF) Power is applied to the substrate holder 164. Alternatively, high frequency (HF) power between 1 W and 10,000 W may be applied to the top electrode 162 and low frequency (LF) power between 0 W and 10,000 W may be applied to the substrate holder 164 . Additional DC bias can be applied to one or more electrodes.

Referring to FIGS. 2B and 2E , the substrate 110 is exposed to a first plasma (block 305 in FIGS. 3A-3C ), resulting in the deposition of a passivation layer 213 on the substrate 110 . The passivation layer 213 may include silicon _oxyfluoride , denoted as _SiOxFy . The thickness, composition, and reactivity of the _SiOxFy layer and subsequent _etch profile depend on the choice of plasma gas composition, substrate material, and processing parameters. Accordingly, the selective etching process can be realized by utilizing these properties of the passivation layer 213 . As shown in FIGS. 2B and 2E , in one example, the passivation layer 213 may be formed preferentially over oxide over nitride under the same process conditions. As a result, passivation layer 213 is significantly thicker over oxide layer 214 in FIG. 2E than over nitride layer 212 in FIG. 2B. This difference in thickness (ie film growth rate) of passivation layer 213 over different materials may be temperature dependent and may be maximized at low temperatures, eg around -65°C. In some embodiments, processing conditions may be optimized such that the formation of passivation layer 213 over a material such as silicon nitride may be negligible or non-existent. Accordingly, the temperature for this step can be adjusted to achieve a desired selectivity, eg, for selectively etching silicon nitride over silicon and silicon dioxide, as described in more detail below in various embodiments.

In one or more embodiments, the overall process cycle may be performed at a temperature lower than or equal to 0° C. for selective plasma etching. As shown in Figures 3A-3C, in such an embodiment, prior to any plasma treatment, the substrate 110 may optionally be cooled to a processing temperature (block 310). The substrate 110 may be cooled using a cooling fluid flowing through the substrate holder 164 . In one or more embodiments, the deposition step (block 305 in FIGS. 3A-3C ) is performed at a low temperature below 0°C, eg, between -120 and 0°C. In other embodiments, processing may be performed at a temperature between -80 and -50°C.

For the etching step, the second plasma is powered by a second gas mixture comprising a noble gas (block 306 in FIGS. 3A-3C ). During the etching step, the substrate 110 is etched by exposure to a second plasma (block 307 in FIGS. 3A-3C ) to remove all or part of the passivation layer 213 . In one case, a thin passivation layer may be removed quickly and the underlying layer may be etched, while in another case, a thick, resistant passivation layer may remain largely unetched, protecting the underlying layer. As noted above, the properties (eg, thickness) of passivation layer 213 are temperature and underlying material dependent, and due to the different properties of passivation layer 213, the etching step may be selective to one material versus another. For example, for the nitride layer 212 (eg, silicon nitride) in FIG. 2B, the passivation layer 213 is so thin that it is etched away and the nitride layer 212 in FIG. 2C is also completely removed. On the other hand, in FIGS. 2E and 2F, the passivation layer 213 formed over the oxide layer is very thick, and substantially no etching may occur, or only a portion of the passivation layer 213 may be removed, leaving the underlying Oxide 214 layers.

In one or more embodiments, the etch step (eg, block 307 in FIGS. 3A-3C ) may be performed at a temperature between -200 and 100°C. In one embodiment, the etching step may be performed at a temperature below 0°C. In a further embodiment, the etching step may be performed at about the same temperature as the deposition step. Performing the deposition step and the etching step at different temperatures can be advantageous to take advantage of the temperature dependence of each process. On the other hand, performing both steps at about the same temperature can advantageously minimize or eliminate the time required to stabilize the temperature.

In one embodiment, to power the second plasma, high frequency (HF) power between 1 W and 10,000 W may be applied to the substrate holder 164, and low frequency (HF) power between 0 W and 10,000 W may be applied. LF) Power is applied to the substrate holder 164. Alternatively, high frequency (HF) power between 1 W and 10,000 W may be applied to the top electrode 162 and low frequency (LF) power between 0 W and 10,000 W may be applied to the substrate holder 164 . Additional DC bias can be applied to one or more electrodes. The plasma processing chamber is maintained at a pressure between 1 mTorr and 1 atm.

In one or more embodiments, multiple iterations of these steps (blocks 304A-307 in FIG. 2A , blocks 304B-307 in FIG. 2B , and blocks 304C-307 in FIG. 2D ) may be performed to achieve desired etching. This is indicated by dashed line C1 in Figures 3A-3C. The duration of each step can vary from 0.01 sec to 10 h. In addition, as indicated by dashed line C2 in FIGS. 3A-3C , in some embodiments, in any of the plurality of cycles, the optional treatment with a hydrogen-containing plasma as described above may also be inserted and included in the cycle process (method blocks 302 and 303).

Although not explicitly described, each of the steps described above (blocks 300-307 in FIGS. 3A-3C ) can be separated by a purge to remove gas from a previous step before starting the next step. For example, a purge between blocks 305 and 306 may be performed to remove the first gas mixture from the plasma processing chamber 120 . For example, purging may be performed by flushing the plasma processing chamber 120 with an inert gas.

2G and 2H show schematic cross-sectional views of the substrate 110 before and after anisotropic plasma treatment, according to an embodiment for spacer etching in self-aligned multiple patterning.

Referring to Figures 2G and 2H, the selective etch nature of the plasma treatment described above can be beneficial in many semiconductor device fabrications, such as silicon nitride spacer etching in self-aligned multiple patterning. In FIG. 2G , the access substrate 110 may include a nitride layer 212 formed over a patterned oxide layer 214 . In one embodiment, nitride 212 includes silicon nitride and is formed as a spacer, and oxide 214 includes silicon oxide and is formed as a mandrel. Spacer etching is performed by anisotropic etching to remove lateral portions of spacer material and leave vertical portions of spacer material on the sidewalls of the mandrel. This is an important but challenging task as the feature sizes of semiconductor devices continue to shrink. As shown in FIG. 2H , using the exemplary method of plasma treatment, removal of the lateral portion of the nitride 212 can be achieved without damaging the oxide 214 or the substrate 110 .

2I and 2J show schematic cross-sectional views of a substrate 110 at intermediate stages during processing to form 3D vertical NAND (VNAND) structures using isotropic plasma processing, according to another embodiment.

In FIG. 21 , substrate 110 and layer stack 216 formed over substrate 110 are shown. Layer stack 216 may include alternating layers of nitride 212 and oxide 214 . In one embodiment, the alternating layers may include silicon nitride and silicon oxide forming a typical 3D VNAND structure. Although layer stack 216 is shown to include a certain number of layers, it may include as few as two layers of nitride 212 and oxide 214 and as many as one hundred or more layers. Additionally, as shown in FIG. 2I , a hard mask layer 218 may be formed over layer stack 216 . In FIG. 2I, a via hole is formed in the middle and filled with a via material 220 to form the via of the formed VNAND memory device. The channel material 220 may include Oxide-Nitride-Oxide (ONO) memory stack and polysilicon material to form a polysilicon channel. Furthermore, according to an embodiment, two slits 222 are formed by etching recesses in the layer stack 216 prior to plasma treatment.

FIG. 2J shows after plasma treatment to selectively remove nitride 212 within layer stack 216 . The plasma treatment can isotropically etch the nitride 212 without damaging the oxide 214 or the substrate 110 , thereby forming lateral voids 224 in the layer stack 216 . Example methods may advantageously etch nitride 212 more selectively and eliminate the need for solution-based processing compared to conventional wet etching using, for example, phosphoric acid. Subsequent processing steps may follow known techniques for forming typical 3D VNAND structures, such as filling the slits 222 and lateral voids 224 with metal materials including aluminum, titanium, tungsten, and the like.

4A shows a process flow diagram 40 for continuous plasma treatment using a plasma comprising fluorosilane, oxygen, and a noble gas, according to an embodiment, and FIG. Process flow chart 42 for cyclic plasma treatment of plasma.

The example method shown in FIG. 4A combines the deposition and etching steps in the previous examples described above and can be performed as a continuous process. In other embodiments, it may also be performed as a multi-step process such as a cyclic process including a hydrogen-containing plasma treatment step as shown in FIG. 4B.

In some embodiments, the plasma etch process may be a continuous process comprising: loading the substrate 110 into the plasma processing chamber (block 400), removing the gas from a gas comprising fluorosilane, oxygen, and a rare gas. The mixture generates a plasma (block 408A), and an etching step is performed by exposing the substrate to the plasma (block 410). As previously stated, the fluorosilane may include tetrafluorosilane (SiF ₄ ). By combining two plasma processes (such as the deposition step and the etch step shown in FIGS. 3A-3C ) into a single plasma process (such as blocks 408A and 410 ), example methods can advantageously simplify the process recipe and shorten the process time.

In one or more embodiments, a separate additional treatment may be performed using a hydrogen-containing plasma. The steps of generating a hydrogen-containing plasma (block 404) and exposing the substrate to the hydrogen-containing plasma (block 406) may be inserted. A gas mixture comprising hydrogen ( _H2 ) or hydrofluoric acid (HF), or ammonia ( _NH3 ), and Ar, He, nitrogen ( _N2 ), or Xe may be used in any proportion. In particular, any ratio of hydrogen:hydrofluoric acid:ammonia can be used. Alternatively, one or more inert gases including argon, helium, nitrogen, or xenon in any proportion may be used.

Referring to FIG. 4B, in some embodiments, the above-described etching steps and treatment with a hydrogen-containing plasma may be repeated cyclically. The cycle can be repeated to achieve the desired etch level. Cycling A cycle of plasma treatment may begin with exposure to a hydrogen-containing plasma (blocks 404 and 406 ) or exposure to a fluorosilane-containing plasma (blocks 408A and 410 ). For plasmas containing hydrogen, gas mixtures containing hydrogen ( _H2 ) or hydrogen fluoride (HF), or ammonia ( _NH3 ), with Ar, He, nitrogen ( _N2 ), or Xe may be used in any proportion. In particular, any ratio of hydrogen:hydrogen fluoride:ammonia can be used. Alternatively, one or more inert gases including any proportion of argon, helium, nitrogen or xenon may be used.

4C shows a process flow diagram 44 for plasma treatment, wherein the plasma used in the plasma treatment comprises hydrofluorosilane, oxygen, and a noble gas, or wherein the plasma comprises silane, a fluorine-containing gas, oxygen, according to another embodiment. , and rare gases.

In FIG. 4C, a different combination of gases may be used (block 408B) than in the embodiment of FIG. 4A or 4B, but with the same process flow as in FIG. 4A or 4B. The plasma treatment shown in FIG. 4C can be performed as a continuous process that can be combined with an optional separate treatment with a hydrogen-containing plasma (eg, FIG. 4A ) or a cyclical repeat of the etch step and treatment with a hydrogen-containing plasma. cyclic processing (eg, Figure 4B) combined. The gas combination can be varied in that hydrofluorosilane or a combination of silane and fluorine-containing gas can be used as the source of fluorine and silicon for the plasma. As explained above in previous embodiments, hydrofluorosilanes may have the formula _SixHyFz , where _x ≠0, _y ≠0, and z≠0. For example, hydrofluorosilane may include trifluorosilane (SiHF ₃ ), difluorosilane (SiH ₂ F ₂ ), or fluorosilane (SiH ₃ F). Silanes may have the formula _SixHy , where _x ≠0 and y≠0. In some embodiments, the silane may comprise monosilane (SiH ₄ ). Fluorine-containing gases may include tetrafluoromethane (CF ₄ ), difluorine (F ₂ ), nitrogen trifluoride (NF ₃ ), sulfur hexafluoride (SF ₆ ), hexafluoroethane (C ₂ F ₆ ), octane Fluorocyclobutane (C ₄ F ₈ ), perfluoroisobutene (C ₄ F ₈ ), fluoroform (CHF ₃ ), or hydrogen fluoride (HF).

In one or more embodiments, the overall process cycle is optionally performed at a temperature lower than or equal to 0° C. to achieve selective plasma etching. In such an embodiment, prior to any plasma treatment, the substrate 110 is cooled to the processing temperature (block 202). In one or more embodiments, the cyclic plasma treatment is performed at a temperature between -120°C and 0°C. In other embodiments, cyclic plasma treatment may be performed at a temperature between -80 and -50°C.

In one or more embodiments, cyclic plasma treatment may be performed using a gas mixture of _SiF4 , _O2 , and a noble gas at any mixing ratio. The rare gas can be Ar, He, Xe, Kr, or Ne. These gases can be used in any combination in any proportion. The process may be operated at a total gas flow into the plasma processing chamber 120 of between 1 sccm and 1000 sccm while maintaining the pressure inside the plasma processing chamber 120 between 1 millitorr and 1 atm. One or more inert gases can be added to the stream as an admixture using Ar, He, Xe, Kr, or Ne in any proportion. In one embodiment, to power the plasma, high frequency (HF) power between 1 W and 10,000 W may be applied to the substrate holder 164, and low frequency (LF) power between 0 W and 10,000 W may be applied. applied to the top electrode 162. Alternatively, high frequency (HF) power between 1 W and 10,000 W may be applied to the top electrode 162 and low frequency (LF) power between 0 W and 10,000 W may be applied to the substrate holder 164 . Additional DC bias can be applied to one or more electrodes. The treatment duration for any step can vary from 0.01 sec to 10 h.

In certain embodiments, an additional gas comprising hydrogen may be added to the first gas mixture of SiF ₄ , O ₂ , and noble gas. In other words, the steps illustrated in blocks 204 , 206 may be performed together with the steps illustrated in block 208 . A gas mixture comprising hydrogen ( _H2 ) or hydrogen fluoride (HF), or ammonia ( _NH3 ), and Ar, He, and nitrogen ( _N2 ), or Xe may be used in any proportion. In particular, any ratio of hydrogen:hydrogen fluoride:ammonia can be used. Alternatively, one or more inert gases including argon, helium, nitrogen, or xenon in any proportion may be used.

Although not explicitly described, each of the steps 200-210 described above may be purged to remove gas from the previous step before starting the next step.

5A-5C show example experimental data for thickness variation of three different substrates after plasma treatment, according to an embodiment. The substrate includes (a) a silicon nitride layer, (b) an amorphous Si (a-Si) layer, or (c) a silicon dioxide layer. Thickness change is a measure of the difference in layer thickness before and after plasma treatment. For example, the thickness of the silicon nitride layer before and after plasma treatment can be measured and compared to calculate the thickness change.

Figure 5A shows experimental data of thickness variation of a substrate comprising a silicon nitride layer, Figure 5B shows experimental data of thickness variation of a substrate comprising an amorphous silicon layer, and Figure 5C shows experimental data of thickness variation of a substrate comprising a silicon dioxide layer data.

For each processing temperature, two data points are presented: (1) thickness change after deposition step using SiF4/ _O2 plasma and ( ₂ ) thickness change after first step and subsequent etching step using Ar plasma . During the deposition step, a thin _passivation film of _SiOxFy was formed on all three substrates, typically with a thickness between 9-15 nm. However, it is clear that the thickness of the deposited film depends on the substrate material, processing temperature, and other processing parameters.

_Notably , the formation of _SiOxFy is minimized or absent at subthreshold temperatures on substrates containing silicon nitride layers (Figure 5A) and on substrates containing amorphous silicon layers (Figure 5B). occur. For example, a thickness of only 1.33 nm was observed on a substrate comprising a silicon nitride layer at -65°C, and a thickness of only 0.14 nm was observed on a substrate comprising an amorphous silicon layer at -100°C. The threshold temperature for such a film thickness transition was found to be higher for substrates comprising silicon nitride layers (approximately -65°C) than for substrates comprising amorphous silicon layers (approximately -100°C).

When the substrate is subsequently exposed to Ar plasma at the same processing temperature, the _SiOxFy layer formed in the previous deposition step can act as a _passivation layer, and as shown in Figures 5A-5C, regardless of the material, Substrate thickness does not substantially change at temperatures above the threshold. In some cases there may even be a slight increase in thickness (eg -40°C in Figure 5A). However, at temperatures below the threshold, presumably due to insufficient passivation, the process enters an etch state to remove material. In the case of substrates comprising silicon nitride layers (FIG. 5A), successful etching occurred below -65°C. In the case of a substrate containing an amorphous silicon layer (Fig. 5B), since the threshold temperature is lower than that of silicon nitride as described above, the etch starts to occur only below -100°C and is not observed at -65°C Substantial thickness variation.

Likewise, as shown in Figure 5C, no etching occurs on SiO2 at -65°C even after Ar plasma treatment.

Referring to Figures 5A-5C, this example emphasizes the effect of temperature in ALE processing to achieve selective etching of materials, especially nitrides over pure elements or oxides. Similar experiments can be performed to optimize and identify temperature thresholds for other material systems.

Next, Figures 6A-6B and Figures 7, 8A-8B will be explained to schematically understand the underlying mechanism of the observed improvements. Such an understanding may facilitate the application of embodiments of the present invention to other material systems without undue experimentation. However, applicants' disclosed processes are not limited in any way by the mechanisms discussed herein. This discussion is not necessarily the only mechanism, and further research may help to understand further underlying mechanisms or alternative mechanisms.

Figure 6A is a graph of the data presented in Figures 5A and 5B to further show the emergence of etch states as the temperature is lowered but after different threshold temperatures for Si3N4 and a _- Si _. Markers with lines represent data after the first SiF ₄ /O ₂ plasma step (deposition), and dots represent data after the subsequent Ar plasma step (etch). The etch state is found at sufficiently low temperatures when the first deposition step does not lead to the formation of _SiOxFy with a thickness _exceeding a few nm.

Schematically, this transition is presented in Figure 6B as a change in deposition rate as a function of processing temperature. For both substrates, the deposition rate decreases as the processing temperature decreases. For a substrate comprising a silicon nitride layer (labeled Si ₃ N ₄ ), such a transformation occurs at a higher temperature than for a substrate comprising an amorphous silicon layer (labeled a-Si). Furthermore, the deposition rate exhibits an inflection point with temperature, in other words, the deposition rate increases and then decreases with decreasing temperature. This trend implies that there may be competing driving forces, thus opening up more potential for future optimization.

Figure ₇ is a series of calculated adsorption energies (E _ad ) of silicon radicals, fluorosilane radical species, and oxygen radicals _on Si and Si3N4 surfaces obtained from density functional theory (DFT) simulations. For example, this energy represents the difference in energy between a system in which the silicon radical is at infinity with respect to the substrate comprising the silicon layer, and a system in which the silicon radical is located on the surface of the substrate comprising the silicon layer. This analysis may reveal possible mechanisms underlying the observed differences in the deposition of _{SiOxFy on Si} and _Si3N4 .

Referring to Figure 7, first, throughout the series, Si and SiF radical species generally have a higher E _ad than oxygen radicals. This would lead to a greater enhancement of the physisorption of _SiFx species than oxygen radicals when the processing temperature was lowered, leading to higher surface concentrations of _SiFx species at lower temperatures. This may explain the initial increase in the deposition rate of _SiOxFy in the _range between 10°C and -40°C shown in Figure 6B.

On the other hand, with a further decrease in temperature, although the surface concentration of _SiF species can be higher, such a high concentration may inhibit the change of _SiF species forming dangling bonds with surface atoms, thereby inhibiting deposition. Therefore, the equilibrium shifts from deposition to etching in the first step, which _explains the _{SiO x} F The loss formed by the _y layer.

Second, as shown in Fig. 7, the adsorption energy (E _ad ) on Si ₃ N ₄ is higher than that on a-Si in the whole series. This may be at least part of the reason behind the higher threshold temperature _of Si3N4 _.

Furthermore, other possible mechanisms that cause differences in the formation of _{SiOxFy layers} between substrates during the deposition steps may also be considered in addition to the above.

Figures 8A and 8B show the surface energies of different complexes calculated using density functional theory.

Referring to FIG. 8A , the -Si-N-Si- surface can adsorb oxygen radicals to form a -Si-NO-Si- surface while reducing its energy to -3.33 eV. This reaction pathway is very favorable due to the lower energy levels of the formed -Si-NO-Si-surface. Subsequently, NO radicals can desorb from the -Si-NO-Si- surface with a relatively low desorption energy of 1.62 eV to form the -Si-Si- surface. Due to the low energy of the NO radicals to be desorbed, the low energy ions can successfully remove the NO radicals from the -Si-NO-Si- surface. In other words, the substrate including the silicon nitride layer can consume oxygen radicals, which can reduce the oxygen concentration in the _{SiOxFy formed} on the silicon nitride layer. _A fluorinated silicon nitride model was used in the calculations to simulate the etch front _of Si3N4.

In addition, if hydrogen is present on the surface of the substrate, this hydrogen can also play a role in the interaction with oxygen radicals. NH groups may be present in the silicon nitride layer which may participate in the deposition mechanism, as a result of residual impurities in the silicon nitride layer or possible hydrogen-containing plasma treatments described in this disclosure.

For example, Figure 8B presents the consumption of oxygen radicals via OH bond formation, the activation energy for the transition state and the desorption energy for OH are both quite low. The *Si-NH-Si* surface can adsorb oxygen radicals and reduce their energy to -0.337 eV, and then release O-H groups through transition states with low potential barriers. Therefore, the *N-H groups in silicon nitride can scavenge oxygen by forming O-H bonds.

Exemplary embodiments of the invention are assembled here. Other embodiments can also be understood from the entirety of the description and the claims made here.

Example 1. A method for processing a substrate, comprising: loading a substrate in a plasma processing chamber; performing a cyclic plasma etch process comprising a plurality of cycles, wherein each cycle of the plurality of cycles comprises: a first gas mixture comprising fluorosilane and oxygen to generate a first plasma; performing a deposition step to form a passivation layer comprising silicon and fluorine by exposing the substrate to the first plasma; generating a second plasma from a second gas mixture comprising a rare gas; and by The etching step is performed by exposing the substrate to the second plasma.

Example 2. The method of Example 1, further comprising maintaining the substrate at a temperature between -120°C and 0°C during the cyclic plasma etch process.

Example 3. The method of either example 1 or 2 further includes: exposing the substrate to a hydrogen-containing plasma before performing the cyclic plasma etching process.

Example 4. The method of any one of examples 1 to 3, wherein each cycle of the plurality of cycles further comprises exposing the substrate to a hydrogen-containing plasma.

Example 5. The method of any one of examples 1 to 4, wherein the first gas mixture further includes a hydrogen-containing gas such that exposing the substrate to the first plasma also exposes the substrate to the hydrogen-containing plasma.

Example 6. The method of any one of Examples 1 to 5, wherein the substrate comprises a first exposed surface comprising silicon nitride, a second exposed surface comprising silicon dioxide, and a third exposed surface comprising silicon, wherein after the cyclic plasma etch process During this process, the first exposed surface is selectively etched relative to the second and third exposed surfaces.

Example 7. The method of any one of examples 1 to 6, wherein the fluorosilane comprises silicon tetrafluoride (SiF ₄ ).

Example 8. The method of any one of examples 1 to 7, wherein the fluorosilane comprises hydrofluorosilane.

Example 9. The method of any one of examples 1 to 8, wherein the hydrofluorosilane comprises trifluorosilane (SiHF ₃ ), difluorosilane (SiH ₂ F ₂ ), or fluorosilane (SiH ₃ F).

Example 10. A method for processing a substrate comprising: taking a substrate comprising a first region including a nitride of a first element, a second region including an oxide of the first element, and a third region The three regions include the elemental form of the first element; and the first region is selectively etched relative to the second and third regions by using a multi-step plasma treatment in a plasma processing chamber, the multi-step plasma treatment comprising: exposing the substrate to a first plasma generated from a first gas mixture comprising silane, a fluorine-containing gas, and oxygen while maintaining the substrate at a first temperature, the first temperature being less than or equal to 0°C; and While the substrate is maintained at a second temperature, the substrate is exposed to a second plasma generated from a second gas mixture including a noble gas.

Example 11. The method of Example 10, wherein the first temperature is lower than the second temperature.

Example 12. The method of either Examples 10 or 11, wherein the first temperature is between -120°C and 0°C, and wherein the second temperature is between -200°C and 100°C.

Example 13. The method of any one of Examples 10 to 12, wherein the silane comprises monosilane (SiH ₄ ), and the fluorine-containing gas comprises tetrafluoromethane (CF ₄ ), difluorine (F ₂ ), nitrogen trifluoride (NF ₃ ), hexafluoromethane Sulfur fluoride (SF ₆ ), hexafluoroethane (C ₂ F ₆ ), octafluorocyclobutane (C ₄ F ₈ ), perfluoroisobutylene (C ₄ F ₈ ), fluoroform (CHF ₃ ), or hydrogen fluoride (HF).

Example 14. The method of any one of examples 10 to 13, wherein the first element comprises Si, Ge, B, W, Al, Ti, Ga, Ta, Hf, or Zr.

Example 15. The method of any one of Examples 10-14, further comprising exposing the substrate to a hydrogen-containing plasma before selectively etching the first region.

Example 16. The method of any one of Examples 10-15, wherein the first gas mixture further includes a hydrogen-containing gas such that exposing the substrate to the first plasma also exposes the substrate to the hydrogen-containing plasma.

Example 17. A method for processing a substrate comprising: taking a substrate comprising a first region including a nitride of a first element, a second region including an oxide of the first element, and a third region The three regions include an elemental form of the first element; and selectively etching the first region relative to the second and third regions by using a plasma treatment comprising: while maintaining the substrate at a first temperature, The substrate is exposed to a plasma generated from a gas mixture including silicon, fluorine, oxygen, and a noble gas at a first temperature lower than or equal to 0°C.

Example 18. The method of Example 17, wherein the plasma treatment is continuous plasma treatment, and wherein the silicon and fluorine in the gas mixture are part of fluorosilane.

Example 19. The method of any one of Example 17, wherein the plasma treatment is cyclic plasma treatment comprising a plurality of cycles in the plasma processing chamber, each cycle of the plurality of cycles comprising exposure to a plasma generated by the gas mixture, and further exposing the substrate to To a hydrogen-containing plasma, and the silicon and fluorine in the gas mixture are part of the fluorosilane.

Example 20. The method of one of Example 17, wherein the silicon in the gas mixture is part of hydrofluorosilane or silane.

While this invention has been described with reference to illustrative embodiments, this description is not intended to be construed in a limiting sense. Many modifications and combinations of the illustrative embodiments, as well as other embodiments of the invention, will be apparent to those skilled in the art upon reference to the description. The appended claims are therefore intended to cover any such modifications or embodiments.

100: Plasma treatment system 110: Substrate 120: Plasma treatment chamber 130: Gas delivery system 140: Vacuum pump system 150: temperature controller 160: the second RF power supply 162: top electrode 164: Substrate bracket 166: Cooler 170: Plasma 180: The first RF power supply 212: Nitride layer, oxide 213: passivation layer 214: Nitride layer, nitride 216: Layer stacking 218: Hard mask layer 220: Channel material 222: Slit 224: Gap 300-307: box C1-C2: dotted line 40-44: Processing flow chart 400-410: box

For a clearer understanding of the present invention and its advantages, reference is now made to the following description in conjunction with the accompanying drawings, in which:

Figure 1A shows a plasma processing tool according to an embodiment of the present application;

2A-2C show schematic cross-sectional views of a substrate during various steps of plasma processing, wherein FIG. 2A shows an incoming substrate including a nitride layer, FIG. 2B shows after a deposition step, and FIG. 2C shows a nitride layer therein, according to embodiments. After the etching step where the layer is removed;

2D-2F show schematic cross-sectional views of a substrate during various steps of plasma processing, wherein FIG. 2D shows an incoming substrate comprising an oxide layer, FIG. 2E shows after a deposition step, and FIG. After the etching step in which the layer is retained;

2G and 2H show schematic cross-sectional views of substrates before and after anisotropic plasma treatment according to yet another embodiment, wherein FIG. substrate, while showing examples of spacer etching in self-aligned multiple patterning, and FIG. 2H shows after anisotropic plasma treatment that selectively removes lateral portions of nitride;

2I and 2J show schematic cross-sectional views of a substrate at an intermediate stage during processing to form a 3D vertical NAND (VNAND) structure by isotropic plasma treatment, according to another embodiment, wherein FIG. 2I shows an oxide layer and A layer-stacked substrate of a nitride layer, and FIG. 2J is shown after an isotropic plasma treatment to selectively remove the nitride;

3A shows a process flow diagram for cyclic plasma treatment on a substrate using a plasma comprising fluorosilane and oxygen, according to an embodiment;

3B shows a process flow diagram for cyclic plasma treatment on a substrate using a plasma comprising hydrofluorosilane and oxygen, according to an alternative embodiment;

FIG. 3C shows a process flow diagram of a cyclic plasma treatment on a substrate using a plasma comprising silane, a fluorine-containing gas, and oxygen;

4A shows a process flow diagram of a continuous plasma treatment using a plasma comprising fluorosilane, oxygen, and a noble gas, according to an embodiment;

4B shows a process flow diagram for a cyclic plasma treatment using a plasma comprising fluorosilane, oxygen, and a noble gas, according to an alternative embodiment;

4C shows a process flow diagram for plasma treatment according to another embodiment, wherein the plasma used in the plasma treatment comprises hydrofluorosilane, oxygen and a noble gas, or wherein the plasma comprises silane, a fluorine-containing gas, oxygen and an inert gas. gas;

5A-5C show exemplary thickness variations of three substrates during a plasma etch process cycle using silicon tetrafluoride and oxygen in the deposition step and argon in the etch step at different process temperatures, according to an embodiment, wherein FIG. 5A shows the thickness variation of silicon nitride, FIG. 5B shows the thickness variation of amorphous silicon, and FIG. 5C shows the thickness variation of silicon dioxide;

6A and 6B show the relationship between the thickness variation and the processing temperature of two substrates (silicon nitride and amorphous silicon) according to the embodiment, wherein FIG. 6A shows the data graph of the thickness variation after each step in the exemplary embodiment, And Figure 6B shows a schematic trend of deposition rates on two substrates as a function of process temperature during the first deposition step;

7 shows, according to an embodiment, the adsorption energies of silicon radicals, tetrafluorosilane radical species, and oxygen radicals on silicon and silicon nitride surfaces calculated from density-functional theory (DFT); as well as

8A and _8B show surface species of mixed oxygen on silicon nitride that may form during the first deposition step of a cyclic plasma etch process, wherein FIG. Example oxygen consumption by a nitride substrate, and Figure 8B shows another example of oxygen consumption via OH bond formation utilizing NH groups that may be present in silicon nitride.

40: Processing flow chart

400-406: box

408A: box

410: box

Claims (20)

A method for processing a substrate, the method comprising: loading the substrate in a plasma processing chamber; performing a plasma etching process including a plurality of cycles, wherein each cycle of the plurality of cycles includes: generating a first plasma from a first gas mixture comprising fluorosilane and oxygen; performing a deposition step to form a passivation layer comprising silicon and fluorine by exposing the substrate to the first plasma; generating a second plasma from a second gas mixture comprising a noble gas; and An etching step is performed by exposing the substrate to the second plasma. The method for processing a substrate of claim 1, further comprising maintaining the substrate at a temperature between -120°C and 0°C during the cyclic plasma etch process. The method for processing a substrate as claimed in claim 1, further comprising: The substrate is exposed to a hydrogen-containing plasma prior to performing the cyclic plasma etch process. The method for processing a substrate of claim 1, wherein each cycle of the plurality of cycles further comprises exposing the substrate to a hydrogen-containing plasma. The method for processing a substrate of claim 1, wherein the first gas mixture further comprises a hydrogen-containing gas, such that exposing the substrate to the first plasma also exposes the substrate to a hydrogen-containing plasma. The method for processing a substrate as claimed in claim 1, wherein the substrate includes a first exposed surface comprising silicon nitride, a second exposed surface comprising silicon dioxide, and a third exposed surface comprising silicon, wherein , selectively etching the first exposed surface relative to the second and third exposed surfaces during the cyclic plasma etch process. The method for processing a substrate as claimed in claim 1, wherein the fluorosilane comprises silicon tetrafluoride (SiF ₄ ). The method for processing a substrate as claimed in claim 1, wherein the fluorosilane comprises a hydrofluorosilane. The method for processing a substrate as claimed in claim 8, wherein the hydrofluorosilane comprises trifluorosilane (SiHF ₃ ), difluorosilane (SiH ₂ F ₂ ), or fluorosilane (SiH ₃ F). A method for processing a substrate, the method comprising: obtaining a substrate comprising a first region comprising a nitride of a first element, a second region comprising an oxide of the first element, and a third region, and the third region contains an elemental form of the first element; and The first region is selectively etched relative to the second and third regions by using a multi-step plasma process in a plasma processing chamber, the multi-step plasma process comprising: While maintaining the substrate at a first temperature, exposing the substrate to a first plasma generated from a first gas mixture comprising a silane, a fluorine-containing gas, and oxygen, the first temperature being less than or equal to 0°C; and While maintaining the substrate at a second temperature, the substrate is exposed to a second plasma generated from a second gas mixture including a noble gas. The method for processing a substrate of claim 10, wherein the first temperature is lower than the second temperature. The method for processing a substrate of claim 10, wherein the first temperature is between -120°C and 0°C, and wherein the second temperature is between -200°C and 100°C. The method for processing a substrate as claimed in claim 10, wherein the silane comprises monosilane (SiH ₄ ), and the fluorine-containing gas comprises tetrafluoromethane (CF ₄ ), difluorine (F ₂ ), nitrogen trifluoride ( NF ₃ ), sulfur hexafluoride (SF ₆ ), hexafluoroethane (C ₂ F ₆ ), octafluorocyclobutane (C ₄ F ₈ ), perfluoroisobutylene (C ₄ F ₈ ), fluoroform (CHF ₃ ), or hydrogen fluoride (HF). The method for processing a substrate as claimed in claim 10, wherein the first element comprises Si, Ge, B, W, Al, Ti, Ga, Ta, Hf, or Zr. The method for processing a substrate as claimed in claim 10, further comprising: The substrate is exposed to a hydrogen-containing plasma prior to selectively etching the first region. The method for processing a substrate of claim 10, wherein the first gas mixture further comprises a hydrogen-containing gas, such that exposing the substrate to the first plasma also exposes the substrate to a hydrogen-containing plasma. A method for processing a substrate, the method comprising: obtaining a substrate comprising a first region comprising a nitride of a first element, a second region comprising an oxide of a first element, and a third region, and the third region contains an elemental form of a first element; and Etching the first region selectively relative to the second and third regions by using a plasma treatment comprising: While maintaining the substrate at a first temperature, exposing the substrate to A plasma of a gas mixture of fluorine, oxygen, and a noble gas, the first temperature being lower than or equal to 0°C. The method for processing a substrate of claim 17, wherein the plasma treatment is a continuous plasma treatment, and wherein the silicon and fluorine in the gas mixture are part of a fluorosilane. The method for processing a substrate as claimed in claim 17, wherein the plasma treatment is a cyclic plasma treatment comprising a plurality of cycles in a plasma processing chamber, each cycle of the plurality of cycles comprising exposure to generating the plasma from a gas mixture and further exposing the substrate to a hydrogen-containing plasma, and wherein silicon and fluorine in the gas mixture are part of a fluorosilane. The method for processing a substrate as claimed in claim 17, wherein the silicon in the gas mixture is a hydrofluorosilane or a part of a silane.

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